Integrated circuits (ICs) have typically been assembled into electronic packages by physically and electrically coupling them to a substrate made of organic or ceramic material. One or more such IC packages can be physically and electrically coupled to a secondary substrate such as a printed circuit board (PCB) or motherboard to form an “electronic assembly”. The “electronic assembly” can be part of an “electronic system”. An “electronic system” is broadly defined herein as any product comprising an “electronic assembly”. Examples of electronic systems include computers (e.g., desktop, laptop, hand-held, server, Web appliance, router, etc.), wireless communications devices (e.g., cellular phones, cordless phones, pagers, etc.), computer-related peripherals (e.g., printers, scanners, monitors, etc.), entertainment devices (e.g., televisions, radios, stereos, tape and compact disc players, video cassette recorders, camcorders, digital cameras, MP3 (Motion Picture Experts Group, Audio Layer 3) players, etc.), and the like.
In the field of electronic systems there is an incessant competitive pressure among manufacturers to drive the performance of their equipment up while driving down production costs. This is particularly true regarding the packaging of ICs, where each new generation of packaging must provide increased performance while generally being smaller or more compact in size. As market forces drive equipment manufacturers to produce electronic systems with increased performance and decreased size, IC packaging accordingly also needs to support these requirements.
In addition, manufacturers of high-end IC packages, such as processors, are experiencing increasing demand for IC packages mounted in thin, light-weight, and/or resilient packaging, because such packaging is useful for many applications. For example, hand-held electronic systems, such as cellular telephones, palm-top computers, personal digital assistants, calculators, MP3 players, watches, hearing aids, and similar equipment typically requires ICs in thin, light-weight, and/or flexible packages.
An IC substrate may comprise a number of layers. Each layer may include a pattern of metal interconnect lines (referred to herein as “traces”) on one or both surfaces. Each layer may also include vias to couple traces or other conductive structure on opposite surfaces of the layer.
An IC substrate typically includes one or more electronic components mounted on one or more surfaces of the substrate. The electronic component or components are functionally connected to other elements of an electronic system through a hierarchy of electrically conductive paths that include the substrate traces and vias. The substrate traces and vias typically carry signals that are transmitted between the electronic components, such as ICs, of the system. Some ICs have a relatively large number of input/output (I/O) terminals (also called “lands” or “pads”), as well as a large number of power and ground terminals.
Surface mount technology (SMT) is a widely known technique for coupling ICs to a substrate. In addition to using SMT to couple an individual IC die to a substrate, it is also well known to use SMT to couple an IC package to a substrate such as a printed circuit board (PCB) or motherboard, using solder bumps, for example.
The formation of conductor features, such as traces and vias, in a substrate typically requires a sequence of complex, time-consuming, and expensive operations that offer ample opportunities for error. For example, forming traces on a single surface of a substrate layer typically requires surface preparation, metallizing, masking, etching, cleaning, and inspecting. Forming vias typically requires drilling, using a laser or mechanical drill. Each process stage requires careful handling and alignment to maintain the geometric integrity of the myriad of traces, vias, and other features. To allow for alignment tolerances, feature sizes and relationships often must be kept relatively large, thus hindering significant reductions in feature density. For example, to provide sufficient tolerance for drilling vias, via pads are typically provided, and these consume significant “real estate”.
Fabrication of a typical multi-layer substrate requires that a large number of process operations be performed. In a known example of a multi-layer substrate, a core layer has a plurality of vias (also referred to herein as “plated through holes” or “PTHs”) and traces. Traces may be formed on one or both surfaces of the core layer. One or more build-up layers, each with traces on one or more surfaces, and typically with PTHs, are formed. The features of the build-up layers can be formed while these layers are separate from the core layer, and the build-up layers may then be subsequently added to the core layer. Alternatively, some features of the buildup layers may be formed after such layers have been added to the core layer.
For the reasons stated above, and for other reasons stated below which will become apparent to those skilled in the art upon reading and understanding the present specification, there is a significant need in the art for methods and apparatus related to electronics packaging that minimize the complexity, time, and cost of fabricating substrates.